1. Field of the Invention
The present general inventive concept relates to a sound reproducing system, and more particularly, to a speaker system to control directivity of a speaker unit using a plurality of microphones and a method thereof.
2. Description of the Related Art
Commonly, one of the characteristics which determines quality of a loudspeaker is directivity. The directivity defines variations in frequency characteristics of sound pressure in different directions of the loud speaker. However, a wider directivity does not automatically ensure the quality of the speaker. It is rather advisable to determine a directivity pattern depending on the purpose of the speaker and the size of the area where the loudspeaker is expected to carry sound. For example, for an audio system, a wide directivity is required. For a public-address system, in order to prevent howling, a narrow directivity wherein the sound is propagated only in certain directions is required. There are other factors to be considered when determining the directivity of the loudspeaker. In a speaker system employing a single speaker unit, the directivity is determined depending on the construction of the unit, that is, whether the speaker unit is a cone speaker or a horn speaker. In a line source speaker system, where a plurality of speaker units are disposed in a linear array, each speaker unit is adapted to emit sound only in a direction determined in accordance with the physical construction and disposition of the speaker units. However, the need to change the directivity of the speaker according to a listening position often occurs.
A conventional directivity control speaker system is disclosed in U.S. Pat. No. 5,953,432 (U.S. application Ser. No. 08/911,183 filed on Aug. 14, 1997 to Yanagawa et al, Line Source Speaker System).
Referring to FIGS. 1A and 1B, a speaker system includes a digital filter array 22, an amplifier array 24 and a speaker unit array 26. The digital filter array 22 includes a plurality of digital audio signal processors (DASPs) DF1-DFm. Each DASP performs filtering of an audio signal input via a first input terminal IN1 and a second input terminal IN2 in accordance with a predetermined digital filter coefficient. The amplifier array 24, which includes a plurality of amplifiers A1-Am, amplifies the audio signals filtered by the digital filter array 22. The speaker unit array 26, which includes a plurality of speakers SP1-SPm in a line source pattern, reproduces the audio signals amplified by the amplifier array 24. Therefore, the directivity of the audio signals is divided into directions S1 and S2 shown in FIG. 1B using the speaker system shown in FIG. 1A. Finally, audio signals input via the first input terminal IN1 and the second input terminal IN2 are reproduced in the directions S1 and S2, respectively.
However, in the conventional speaker system shown in FIG. 1A, directivity cannot be obtained in accordance with a listening position because an exact listening position measuring method for speaker driving is not provided, and since filters and amplifiers are included in each speaker unit, the conventional speaker system must include a special heat sink component.
Also, even if a speaker system with a multiple channel driver has an advantage in power handling, when a high frequency signal is reproduced, various lobes are generated, where each lobe represents a same sound pressure and depends on a wavelength of a reproducing frequency band and a distance between channel drivers. Accordingly, as shown in FIG. 2A, listening positions where frequency quality is flat and listening positions where the frequency quality is not flat exist. FIG. 2B is a graph illustrating frequency quality in a sweet spot and an off axis. The frequency quality in the sweet spot, which is an optimal position where a directive lobe exists, is flat over the entire frequency band, however, the frequency quality in the off axis has a problem that a sound pressure is not flat in certain bands.